In the operation of multi-cylinder diesel engines, such as, for example, locomotive engines which may have 12, 16, or even 20 cylinders, it is sometimes difficult to determine if an individual cylinder is not firing or is producing too little or too much power. Attempts to determine this by shutting off fuel to one of the cylinders and observing how much the length of the injection period is changed on the remaining cylinders has produced inconsistent results because the change in the length of injection duration has been small compared to the adjustments being made to maintain engine rpm. In other words, the relatively small fuel rate changes required in the remaining operating cylinders are not easily accurately measured so that the power of the non-operating cylinder is not accurately determined. As a result, a more satisfactory method was desired.